Underdrive-type press

ABSTRACT

[Object] An underdrive-type single action press capable of saving energy, saving space, and realizing high-precision formability in a well-balanced manner is provided. Particularly, a press capable of shortening a forming stroke, reducing overall height, exactly correcting the deflection of the slide or dies to improve adhesion of the dies to a workpiece, and realizing pressure equalization of a wrinkle holder is provided. 
     [Means for Resolution] An underdrive-type press includes a forming press unit including a lower die located inside an annular wrinkle holder fixedly disposed on a bed, and a drive mechanism disposed within the bed to raise or lower a slide supporting the lower die, a slide raised or lowered by a drive mechanism loaded on the side of a crown, a die-clamping press unit including an upper die having a clamping portion pinching a workpiece in cooperation with the wrinkle holder at its peripheral edge, and a device applying a pressing force to the upper die from its back after the last stage of the descent of the slide of the die-clamping press unit and the upper die for improvements in forming precision.

TECHNICAL FIELD

The present invention relates to a press used for plastic forming of ametal material or nonmetal material, and particularly, to anunderdrive-type high-precision forming press.

BACKGROUND ART

Presses are widely used as a means to perform plastic formingrepresented by drawing on metal and nonmetal materials. In asingle-action type of such presses, generally, a frame structure inwhich a column is erected on a bed, and a crown is installed at the apexof the column is adopted. As shown in FIG. 1, a slide f on which anupper die (die in this example) e is loaded is adapted to be raised orlowered by a driving device (not shown) provided on the side of thecrown. A lower die (punch in this example) g is fixed to the bed, and awrinkle holding ring h is disposed around the lower die g. The wrinkleholding ring h is supported by a number of cushion pins m extending froma pad k which is raised or lowered by fluid pressure cylinders j.

In this press, as shown in FIG. 1, a forming stroke is performed byraising the pad k to lift the wrinkle holding ring h to the level of thelower die by the cushion pins m, lowering the slide to sandwich aperipheral edge of a workpiece W by the wrinkle holding ring h and aperipheral edge of the upper die e, further pressing and lowering theslide f in this state, and lowering the wrinkle holding ring h in aninterlocking manner.

However, in the conventional press, the upper slide side becomes aforming press unit, and the slide is lowered by a whole stroke requiredfor forming, by a drive mechanism. Thus, stroke length becomes large,and achievement of energy saving is difficult. Further, since the strokelength is large, the overall height of the press becomes high, andthereby, a large space is required within a building. In some case, asituation in which installation cannot be made also occurs.

Moreover, in a case where products to be press-formed are, for example,panels, such as vehicle bodies or doors of transportation meansrepresented by automobiles, enlargement and complication of shapes, anddevelopment of materials progress, and accordingly, requirements for theprocessing precision of the press are becoming very high.

In order to cope with this, conventionally, the dies are processed withhigh precision, a frame structure whose rigidity has become high isadopted, or a CNC control method is adopted for operation of the press.However, any deflection by elastic deformation and occurrence oftroubles resulting therefrom could not be avoided due to a large loadduring forming operation.

That is, deflection δ1 is caused in the slide as shown in FIG. 1 due toa large forming load. This impairs close contact between the slide andthe upper die. Thus, it is difficult to uniformly transmit a formingforce to the workpiece, and the uniform contact on a die cavity of theworkpiece becomes is hardly performed. Therefore, forming precisiondeteriorates.

Further, in the conventional press, the wrinkle holding ring issupported by the die cushion pins with a pitch of 150 to 300 mm, andsuch cushion pins have dimensions such that they extend to pass througha bolster. For this reason, it is unavoidable that deflection δ2 iscaused in a wrinkle holding ring between the cushion pins due to acompressive load by the slide. For this reason, nonuniformity of awrinkle holding force occurs, and poor forming precision, such as areduction in plate thickness or generation of a shocking line is easilycaused.

In addition, in the conventional press, a hydraulic ram type drivemechanism or a crank type drive mechanism is adopted as a drivemechanism of the slide. Since the former cannot take a large number ofstrokes per unit time, realization of high throughput is difficult.Although the latter can make processing speed and the number of strokeshigh, there are problems in that processing force, processing speed,stroke position, etc., cannot be set arbitrarily, that the motion of theslide is limited, that slide speed cannot be adjusted according tovarious conditions, such as forming shapes or sizes of products, ormaterials, and that output according to the stroke length of the slidecannot be adjusted.

Thus, the present applicant has suggested a link motion pres's inJapanese Unexamined Patent Application Publication No. 2001-300778. Inthis link motion press, a slide is adapted to ascend and descend via atoggle link mechanism, and a servo motor and a screw nut are used as adriving means of the toggle link mechanism. This press has advantages inthat the processing speed and the number of strokes can be made high,the processing speed, stroke, and output can also be set arbitrarily.

However, the above prior art is ineffective in improvements in thenonuniformity phenomenon of the wrinkle holding force resulting from theaforementioned deflection, and in the deflection phenomenon of theslide. Further, the slide is lowered by a whole stroke required forforming. Thus, stroke length becomes large, and achievement of energysaving is difficult. Further, the length of a screw shaft affects theheight of the press, and the screw shaft becomes long as the stroke ofthe slide becomes long. Therefore, there is a problem in which theoverall height of the press becomes high.

Patent Document 1: JP-A-2001-300778

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

The invention has been made in order to solve the above problems. It isthus a first object of the invention to provide an underdrive-typesingle action press capable of saving energy, saving space, andrealizing high-precision formability in a well-balanced manner.

It is a second object of the invention to provide an underdrive-typesingle action press capable of realizing high throughput (high cycletime) in addition to the above object.

Means for Solving the Problem

In order to achiever the above first object, an underdrive-type pressincludes an annular wrinkle holder fixedly disposed on a bed; a formingpress unit including a lower die located inside the wrinkle holder, aslide supporting a lower die within the bed, and a drive mechanismraising or lowering the slide; a drive mechanism loaded on the side of acrown, and a slide raised or lowered by the drive mechanism; adie-clamping press unit including an upper die having a clamping portionpinching a workpiece in cooperation with the wrinkle holder at itsperipheral edge; and a device applying a pressing force to the upper diefrom its back after the last stage of the descent of the slide of thedie-clamping press unit and the upper die for improvements in formingprecision.

ADVANTAGE OF THE INVENTION

In the invention, the die-clamping press unit is disposed on the crownside, the forming press unit is disposed on the bed side, thedie-clamping press unit is not lowered under pressure during descent,and a stroke length only for performing die-clamping is required. Thus,the overall height of the press can be made low. Further, forming isperformed by raising a lower forming press to pressurize the lower diein a state where the die-clamping press unit operates and the upper dieabuts on the wrinkle holder. Thus, a minimum stroke equal to the formingstroke will be sufficient for the stroke length of the forming pressunit. As a result, energy saving can be realized.

Moreover, since the wrinkle holder does not ascend or descends whilebeing supported by the cushion pins, but is fixed in position on thebed, deflection of the wrinkle holder between the pins does not occursunlike the conventional press. In addition, a device for improvements informing precision is provided on the side of the die-clamping pressunit, and a pressing force is positively superimposed on the upper diefrom its back after the last stage of the descent of the die-clampingpress unit. Thus, at least one of optimization of the wrinkle holdingforce by the upper die clamping portion and the wrinkle holder, andcorrection of deflection on the side of the slide can be achieved, andthereby, the forming precision of products can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing the outline and deflection generationsituation of a conventional single-action-type press.

FIG. 2 is a partial cutaway front view showing a first embodiment of anunderdrive-type press of the invention.

FIG. 3 is a longitudinal sectional front view showing the details ofFIG. 2.

FIG. 4 is a partially enlarged view of FIG. 3.

FIG. 5 is a partially enlarged view showing an example of a pressurizingportion and a pressing member in a forming precision improving device.

FIG. 6 is a partially enlarged view showing another example of thepressurizing portion in the forming precision improving device.

FIG. 7 is an explanatory view showing an example of a pressuregenerating means in the forming precision improving device.

FIG. 8 is an explanatory view showing another example of the pressuregenerating means in the forming precision improving device.

FIG. 9 is a system diagram showing a pressure control means in theforming precision improving device.

FIG. 10A is a sectional view showing the operation of the firstembodiment in a stepwise fashion, and showing a last stage state beforethe start of forming.

FIG. 10B is a sectional view showing the operation of the firstembodiment in a stepwise fashion, and showing a state where a lower dieand an upper die are matched together, and a wrinkle holding force isapplied.

FIG. 10C is a sectional view showing the operation of the firstembodiment in a stepwise fashion, and showing a last stage state wherethe lower die has ascended to perform forming.

FIG. 10D is a sectional view showing the operation of the firstembodiment in a stepwise fashion, and showing a state where the formingis completed, and the upper die has ascended.

FIG. 11A is a sectional view showing a state of the forming precisionimproving device when the upper die has touched a wrinkle holder.

FIG. 11B is a sectional view showing a state of the forming precisionimproving device during forming.

FIG. 12 is an enlarged view of the state of FIG. 10B.

FIG. 13 is an enlarged view of the state of FIG. 10C.

FIG. 14 illustrates an example of a stroke and pressure diagram of apress to which the invention is applied.

FIG. 15 is a front view showing another example of a slide drivemechanism of a forming press unit.

FIG. 16A is a sectional view showing the operation when the slide drivemechanism of FIG. 15 is used, in a stepwise fashion, and showing a statebefore the start of forming.

FIG. 16B is a sectional view showing the operation when the slide drivemechanism of FIG. 15 is used, in a stepwise fashion, and showing a statewhere the lower die and the upper die are matched together, and thewrinkle holding force is applied.

FIG. 16C is a sectional view showing the operation when the slide drivemechanism of FIG. 15 is used, in a stepwise fashion, and showing a laststage state where the lower die has ascended to perform forming.

FIG. 16D is a sectional view showing the operation when the slide drivemechanism of FIG. 15 is used, in a stepwise fashion, and showing a statewhere the forming is completed, and the upper die has ascended.

FIG. 17 is a front view showing a second embodiment of the invention.

FIG. 18 is a partially enlarged view of FIG. 17.

FIG. 19 is a plan view of the device of FIG. 17.

FIG. 20A is a sectional view showing another aspect of the pressurizingportion and the pressing member in the second embodiment.

FIG. 20B is a plan view of FIG. 20A.

FIG. 21 is a front view showing an example in which the direction of thepressing member of the second embodiment is reversed.

FIG. 22 is a front view showing a third embodiment of the invention.

FIG. 23 is a sectional view taken along a X-X line of FIG. 22.

FIG. 24A is a sectional view of a portion where adjustment pieces areused in the aspect of FIG. 22.

FIG. 24B is a sectional view of a portion where the adjustment piecesare not used in the aspect of FIG. 22.

FIG. 25 is a front view showing an example in which the direction of thepressing member of the third embodiment is reversed.

FIG. 26 is a partially enlarged view of FIG. 25.

REFERENCE NUMERALS

-   2: FORMING PRESS UNIT-   2 a: SLIDE-   2 b: DRIVE MECHANISM-   2 e: ECCENTRIC LINK-   2 f: DIGITAL SYSTEM MOTOR-   3: DIE-CLAMPING PRESS UNIT-   3 b: DRIVE MECHANISM-   3 d: SLIDE-   3 e: TOGGLE LINK-   3 f: DIGITAL SYSTEM MOTOR-   5: FORMING PRECISION IMPROVING DEVICE-   5 a: BASE-   5 b: PRESSURIZING PORTION-   5 b 1: FIRST PRESSURIZING PORTION-   5 b 2: SECOND PRESSURIZING PORTION-   5 c: PRESSURE GENERATING MEANS-   5 c 1: FIRST PRESSURE GENERATING MEANS-   5 c 2: SECOND PRESSURE GENERATING MEANS-   5 e: PRESSING MEMBER-   5 e 1: FIRST PRESSING BODY-   5 e 2: SECOND PRESSING BODY-   A: LOWER DIE-   B: UPPER DIE

PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION

Preferably, the device applying a pressing force to the upper die fromits back for improvements in forming precision includes a disk-like basedisposed between a lower surface of the slide and the upper die; apressurizing portion built in the base; a pressing member having apressing surface against the lower surface of the slide or the backsurface of the upper die, and an opposite surface to the pressingsurface facing the pressurizing portion; a pressure generating meansdisposed in a place outside the base to feed a pressurizing medium tothe pressurizing portion; and a means disposed in a place outside thebase to control the pressure of the pressurizing medium fed to thepressurizing portion from the pressure generating means.

If this construction is adopted, the pressing member protrudes topowerfully press the lower surface of the slide or the back surface ofthe upper die by feeding a pressurizing medium to the pressurizingportion from the pressure generating means, and then concave deflectionof the slide is corrected. Thereby the slide and the upper die arebrought close contact with each other, so that the forming force can beuniformly transmitted to a workpiece, and the pressure of the surfacesof the upper and lower dies which abut on the workpiece is equalized.For this reason, since a material flow state becomes uniform, theforming shape of a workpiece can be improved.

Further, since a means is provided to control the supply pressure of apressurizing medium to the pressurizing portion by the pressuregenerating means, the force of the pressing member can be controlledaccording to a press stroke. Thereby, the wrinkle holding force to aworkpiece can be controlled to an optimal magnitude, and the force ofthe pressing member is strengthened at a final forming stage, so thatdeflection of the slide can be corrected. Moreover, since the baseincluding the pressing member and the pressurizing portion becomes aflat unit, structure is easy, and installation to the press is alsoeasy.

In the invention, the pressurizing portion is composed of a chamber bodyand an elastic body built in the chamber body, or is composed of achamber body and a fluid which fills the chamber body.

According to the former, since the elastic body is expanded by apressurizing medium to move the pressing member, sealing is easy.Further, according to the latter, since the pressing member is directlypressurized, sensitivity becomes good, and pressure control is alsoeasy.

Preferably, the pressure generating means has a servo motor as a drivingsource.

According to this, the pressure of the pressurizing portion which movesthe pressing member can be freely controlled with precision, and optimaleffects adapted to the degree of deflection, the material properties ofworkpieces, plate thickness, etc. can be obtained.

A sensor for adjusting the pressure to be fed to the pressurizingportion from the pressure generating means is interposed between thelower surface of the slide and the back surface of the upper die orbetween the base and the back surface of the upper die.

According to this, since control to an optimal pressure can be made inresponse to the state of deflection deformation, correction accuracy canbe improved.

Depending on circumstances, the invention includes an aspect in whichthe pressing member and the pressurizing portion are composed of fluidpressure cylinders, and these cylinders are disposed within the base atpredetermined intervals.

According to this, since a predetermined number of small pistoncylinders may be arrayed within the base, the fabrication of theapparatus is easy. Further, if a plurality of rows of piston cylindersare disposed in the width direction of the chamber body, the deflectioncorrection force and the wrinkle holding force can be adjusted morefinely.

Other preferable aspects in the invention are as follows.

1) The pressing member has one disk shape with a size enough to cover awrinkle holding region.

According to this, structure is easy, and fabrication is also easy.

2) The pressing member has a first body in its central region, and asecond body in a position corresponding to the wrinkle holding region,the pressurizing portion is composed of a first pressurizing portioncorresponding to the first body, and a second pressurizing portioncorresponding to the second body, and the pressure generating means iscomposed of a first pressure generating means for the first pressurizingportion, and a second pressure generating means for the secondpressurizing portion.

According to this, pressurization for the wrinkle holder, andpressurization for deflection correction can be controlledindependently, and an optimal wrinkle holding force, and optimaldeflection correction of the slide can be realized according to a pressstroke.

Here, aspects of the above 2) includes a case where the first body has adisk shape, and the second has an annular flame shape in plan view, anda case where the first body has a disk shape, or the first body and thefirst pressurizing portion are composed of a plurality of fluid pressurecylinders which are connected with each other and are arranged atrequired intervals, and the second body and the second pressurizingportion are composed of a plurality of fluid pressure cylinders whichare connected with each other and are arranged at required intervals.

According to these, control to an optimal wrinkle holding force adaptedto properties and forming conditions of workpieces can be made.Particularly, in a case where the second body and the secondpressurizing portion are composed of a plurality of fluid pressurecylinders which are connected with each other and disposed at requiredintervals, the magnitude of the wrinkle holding force can be adjustedlocally and simply, and an optimal wrinkle holding force suited to thematerial, size, etc. of workpieces can be obtained.

Preferably, the drive mechanism of the die-clamping press unit includesa digital system motor and links, and the drive mechanism of the formingpress unit includes a digital system motor and links.

According to this, since an ascent/descent position, a stroke,processing speed, and output can be set arbitrarily and can becontrolled correctly, the number of strokes can be made significantlyhigh. Particularly, in a case where eccentric links are used for thedrive mechanism of the forming press unit, the drive mechanism isrotary, and does not have stop time. Thus, for example, high cycle timeof about twice that of the servo press in the prior art can be obtained.

Although other features and advantages of the invention will be madeclear from the following detailed description, it is apparent that theinvention is not limited to the constructions shown in the embodimentsas long as they include basic features of the invention, and variouschanges and modifications thereto can be made.

Embodiment 1

Hereinafter, embodiments of the invention will now be explained withreference to the accompanying drawings.

FIGS. 2 and 3 show a first aspect of an underdrive-type digital drivingpress according to the invention. Reference numeral 1 represents a pressframe which has a bed 1 a, a plurality of columns 1 b, and a crown 1 c.The center of the bed 1 a is equipped with a forming press unit 2, andthe crown is equipped with a die-clamping press unit (upper press unit)3. A bolster 4 is disposed on an upper surface of the bed.

The forming press unit (lower press unit) 2 includes a lower die A, aslide 2 a disposed in a hole in the bed, and a drive mechanism 2 b forraising or descending the slide. In the drive mechanism 2 b, preferably,a digital system motor 2 f, such as a servo motor or a CNC motor, and apair of right and left eccentric links 2 e which are driven by thismotor are used.

In detail, the eccentric links 2 e have first levers 201 ends of whichare respectively supported in eccentric positions of a pair of right andleft rotating disks 200 and 200, second levers 202 rear ends of whichare linked to free ends of the first levers 201 and the other ends ofwhich are linked to the slide 2 a, and third levers 203 rear ends ofwhich are linked to the free ends of the first levers 201 and the otherends of which are fixed to the bed. The rotating disks 200 and 200 havegears at their outer peripheries, respectively, and are adapted to berotated in opposite directions by a large gear driven by a driving gearof the digital system motor 2 f, a small gear in the center of thislarge gear, and a small gear meshing with this small gear.

The lower die (punch) A is located at an upper surface of the bolster 4,and the lower die A is linked with an upper portion of the slide 2 a viaa linking block which extends via an opening of the bolster 4.

An annular wrinkle holder 7 which places a plate-like workpiece W isfixed to the upper surface of the bolster 4, and a distance block 8which once catches an upper die B during the descent of the upper die,thereby regulating a stroke, is installed on the bolster outside thewrinkle holder 7. The distance block 8 may be formed in the shape of aframe on the whole and may be a plurality of split single bodies(columns or walls). However, in any case, the height of the distanceblock is set to a dimension which is equal to or moderately higher thana level in a state where the workpiece W is disposed on the wrinkleholder 7 before start of forming.

In addition, in this embodiment, in order to attain the balanced ascentof the lower die A, guide pins 21 are implanted at predeterminedintervals around the linking block of the slide 2 a, and longitudinalholes 41 which allows insertion/removal of the guide pins 21 aredisposed in the bolster 4. Also, in order to stabilize theascent/descent movement of the lower die A, push-up pins 42 which arepressed by the guide pins 21 are inserted into the longitudinal holes 41corresponding to a lower surface of the lower die A.

The die-clamping press unit 3 has a slide 3 d and a drive mechanism 3 bfor raising or descending this slide. Although the drive mechanism 3 bmay be the same as the drive mechanism of the forming press unit 2, itis preferable that high-speed descent and a large die-clamping force areobtained. Thus, in this embodiment, a pair of right and left togglelinks 3 e and 3 e, and a digital system motor (for example, an AC servomotor, etc.) 3 f are used.

Each toggle link 3 e has a first link 301 one end of which is linked toa nut 300 which is screwed to a screw shaft 304 rotated by the motor 3f, a second link 302 one end of which is linked to the crown, and athird link 303 one end of which is linked to the slide 3 d, and theother ends of the links are collected and linked together by pivots.

Also, a means which exhibits a slide deflection correcting functionor/and a wrinkle holding pressure-equalizing function for improvementsin forming precision is provided in the die-clamping press unit 3 andits vicinity. Specifically, the slide 3 d of the die-clamping press unit3, and a device 5 which applies a pressing force to the upper die B frombehind after the last stage of the descent of the upper die B areprovided. This significantly differs from a normal press in which anupper die (die) B is only fixed to the lower surface of the slide 3 d.

The device (hereinafter referred to as forming precision improvingdevice) 5 has a main body interposed between the lower surface of theslide 3 d, and the upper die B. The main body includes a disk-likerelatively flat base 5 a, a pressurizing portion 5 b built in the base 5a, and a pressing member 5 e an end surface of which faces the lowersurface of the slide 3 d in this embodiment, and which has a portionbelow the slide built in the pressurizing portion 5 b so that it canascend or descend. Outside the device, a pressure generating means 5 cwhich supplies and discharges a pressurizing medium to and from thepressurizing portion 5 b, and a control means 5 f which controls thedriving of the pressure generating means 5 c are provided. The pressuregenerating means 5 c is loaded on, for example, the column 1 b.

Since the base 5 a functions as a base, it is made of a thick plate,etc. so as to have high strength and rigidity. As shown in FIG. 4, theportion of the base outside the pressurizing portion 5 b is suspended bya damper 3 g mounted on the slide 3 d so that there may be a moderategap S from the lower surface of the slide 3 d in a normal state. Theclamper 3 g has an arm 31 with a hook which is engaged with anddisengaged from a hanging portion provided at a side end of the base 5a.

Although the upper die B is suspended by an L-shaped suspension means 11fixed to an edge of the base 5 a, the upper die may be directly fixed tothe base 5 a. In a case where the suspension means 11 is used, a guide110 as shown in FIG. 4 may be attached so that any deviation may notoccur in the horizontal direction of the upper die B.

The pressurizing portion 5 b is of a direct type in this embodiment. Asshown in FIG. 5, the pressurizing portion is formed inside the base 5 aas a relatively shallow flat chamber 5000, and is adapted such that apressurizing medium is directly introduced or discharged through achannel 52 provided in a proper place of the base 5 a. Although liquids,such as oil and water, are generally used as the pressurizing medium,gas is also used depending on circumstances.

To explain the pressurizing portion 5 b in detail, the base 5 a isintegrated, for example, by fastening the main body 50 and a lid 51 witha fixing element. A recess 500 is formed in the main body 50, and arecess which faces the recess 500 is formed in the lid 51, therebyconstituting a flat chamber. The lid 51 is formed with an opening 511which communicates with the recess but has a smaller width than therecess. Since the pressurizing medium is directly introduced ordischarged through the channel 52 as mentioned above, a sealing member5100 which touches a peripheral wall portion of the pressing member 5 eis attached along an inner wall surface of the opening 511.

The pressing member 5 e is made of one disk-like body (plate) which hasalmost the same area as the area of the workpiece W in this embodiment.The portion of the pressing member below a pressing end surface 520 isfitted into the opening 511, and extends within the recess. A lower endlateral portion of the pressing member is provided with a flange 521which can contact with the top wall of the recess. This flange and aceiling wall are adapted to define a stroke ST to a range of, forexample, 1 to 5 mm. Arrows of FIG. 5 indicate a state where apressurizing medium is injected into the chamber 5000 through thechannel 52, and thereby the pressing member 5 e protrudes and the endsurface 520 presses the slide 3 d.

In addition, the pressurizing portion 5 b is not limited to the directtype. FIG. 6 shows an example of an indirect type which is constitutedby a chamber 5000 defined by a recess, and an elastic body 5001 built inthe chamber.

The elastic body 5001 is made of contractable or expandable material,such as rubber. An upper surface of the elastic body 5001 may be joinedto the pressing member 5 e. In addition, in this embodiment, a flat bagis used as the elastic body 5001 a portion of which is connected to thechannel 52 of the base 5 a via a joint. However, the elastic body 5001is not limited to a material as long as it is expanded by the pressureof the pressurizing medium to generate pressure, and liquid, pasty, orsolid rubber may be used.

The pressure generating means 5 c is a means which makes a pressurizingmedium, and feeds and discharges the medium through the channel 52 toand from the pressurizing portion 5 b. Preferably, adigital-controllable-type pressure generating means is used. FIG. 7shows a cylinder-type pressure generating means as an example of thepressure generating means 5 c. A branch pipe 540 connected to apressurizing-side outlet of a cylinder 55 is connected to a pipe 54connected to the channel 52 via a pump 53 and a check valve. A nut 56 isscrewed to a screw 5501 of a piston rod 550 inserted into the cylinder55. This nut 56 itself is connected with a rotational member (smallpulley or pinion) 571 of an output part of a servo motor 57 by atransmission means, directly or via a rotational member (pulley or smallgear) 560 for deceleration.

In this type, the output of the servo motor 57 is decelerated, andtransmitted to the nut 56, the piston rod 550 is moved by the rotationof the nut 56, and thereby, the pressure of a system composed of thebranch pipe 540 and the pipe 54, which are filled with a fluid from thepump 53 in advance, is controlled toward its increased side or reducedside. As such, as the movement direction and speed of the piston rod 550change depending on the rotational direction, rotational frequency ortorque of the servo motor 57, the pressure of the pressurizing portion 5b is changed and the projecting force and pressing force of the pressingmember 5 e changes.

The pressure generating means 5 c is not limited to the cylinder type.FIG. 8 shows a pump-type pressure generating means. In this type, as thepump 53 is driven by the servo motor 57, the internal pressure in thepipe 54 which leads to the channel 52 is controlled to its increasedside or reduced side. That is, the pressure generating means includesthe pump 53 which is interposed in the pipe 54 to supply a pressurizingmedium, for example, pressure oil, to the pressurizing portion 5 b froma tank depending on the rotational direction, and on the contrary,returns the pressurizing medium to the tank from the pressurizingportion 5 b, and the servo motor 57 which drives the pump normally orreversely, and controls the force created by the pressurizing portion 5b depending on the rotational direction, torque, and speed control.

In this type, the pressing member 5 e ascends as the pressurizing mediumwithin the tank is fed to the pressurizing portion 5 b through the pipe54 and the channel 52 from the pump 53 by the normal direction drivingof the servo motor 57. Further, if the servo motor 57 is driven in thereverse direction, the pump 53 sucks the pressurizing medium of a pipe,and the oil in the pressurizing portion 5 b and pipe 54 is returned tothe tank. Thus, the pressing member 5 e descends. Accordingly, thepressing force of the pressing member 5 e can be arbitrarily controlledwith precision by the control of the torque and speed of the servo motor57.

The pressure control means 5 f is disposed as a control panel, etc. in aproper place in the vicinity of the bed, the column, etc. in order tocontrol the driving of the pressure generating means 5 c. The pressurecontrol means 5 f, as shown in FIG. 9, is constituted as a computerincluding a controller like a CNC. Also, in order to detect the deformedstate of the slide 3 d or the upper die B, as shown in FIGS. 3 to 6, asensor 5 g is attached to a central region between the lower surface ofthe base 5 a and the upper die B, or a predetermined part, such as alateral part, and is electrically connected to the controller. As thesensor 5 g, displacement sensors represented by a distortion sensor, apressure sensor, etc. which can detect compression and tension, areused. Furthermore, a position sensor may be used.

Further, a pressure sensor 5 h is interposed in a system of the pressuregenerating means 5 c. An output system of the pressure sensor 5 h and ofthe displacement sensor 5 g along with an output system of speed andtorque of the servo motor 57 is connected to the controller. The kinds,properties, processing conditions, etc., of workpieces are input to andstored in a computer, and instructions on rotational direction, speed,and torque are issued from the controller in response to calculatedsuitable conditions.

Also, rotational frequency and torque are fed back to the controllerfrom the output system of the servo motor 57. Further, the actualdeflection state (compression and tension) of the slide 3 d or the upperdie B is detected by the sensor 5 g, cushion pressure is detected by thepressure sensor 5 h, and the deflection state and cushion pressure arefed back to the controller. Accordingly, the rotational direction,speed, and torque which are sequentially compared with proper values,and calculated, and which are corrected if there is any difference willbe ordered to the servo motor 57.

Next, the operation and effects of the above embodiment will beexplained.

FIGS. 10A to 10D, and FIG. 11A, FIG. 11B, FIG. 12, and FIG. 13 show theoperation of the press shown in FIG. 3 in a stepwise fashion, and FIG.14 shows a stroke and pressure diagram. FIG. 10A shows a state beforestart of processing. The upper die B and the lower die A are at retreatlimits. At this time, any deformation of the slide 3 d or the upper dieB is not caused. Thus, a distortion generation signal is not issued fromthe displacement sensor 5 g in the forming precision improving device 5,but the pressure of the pressurizing portion 5 b is set to zero to lowpressure. A gap S exists between the upper surface of the base 5 a ofthe forming precision improving device 5 and the lower surface of theslide 3 d, as shown in FIG. 4. On the other hand, the workpiece w ismounted on the wrinkle holder 7, and the upper end surface of thedistance block 8 is at almost the same level as the upper surface of theworkpiece W.

Next, if the motor 3 f is driven to operate the die-clamping press unit3, the slide 3 d and the upper die B are lowered, and as shown in FIG.10B, the upper die B abuts on the wrinkle holder 7 and the distanceblock 8. Thereby, as shown in FIG. 11A, the suspended base 5 a ispressed upward, and its upper surface touches the lower surface 320 ofthe slide 3 d. If the sensor 5 g detects this touch state, a signal isdelivered from the control means 5 f which has received the detectionsignal, and the pressure generating means 5 c operates, and thereby, thepressurizing medium is fed to the pressurizing portion 5 b via the pipe54 and the channel 52.

Thereby, since the pressurizing portion 5 b is boosted to the pressureP1, as shown in FIG. 11B, the pressing surface 520 of the pressingmember 5 e rises by a prescribed height, for example, 1 to 4 mm, fromthe level of the upper surface of the base. Thereby, a reaction force isapplied to the upper die B. This state is shown in FIG. 10B and FIG. 12.Since a uniform wrinkle holding force acts on the whole surface of thewrinkle holder 7, the uniform wrinkle holding force is applied to theworkpiece W between the upper die B and the wrinkle holder 7.

In this state, by operating the drive mechanism 2 b of the forming pressunit 2, and expanding the eccentric links 2 e, the slide 2 a is raised,and the lower die A is raised from the bolster 4.

That is, since a large gear is rotated by a drive gear by the driving ofthe digital system motor 2 f and the one pair of rotating disks 200 and200 are rotated by a small gear in the center of the large gear, thefirst lever 201 and 201 advance in the expansion direction, and thesecond lever 202 and the third lever 203 rise. Thereby, the slide 2 a ispushed up within the bed, and the lower die A connected to the block inthe center of the slide ascends. An ascent stroke at this time islow-speed→high speed as shown in FIG. 14.

In addition, during the ascent of the slide 2 a, the guide pins 21advances into the holes 42 of the bolster 4, and the pins 42 insertedinto the holes 42 of the bolster 4 are pushed up, stable balanced ascentis guaranteed.

As such, if the slide 2 a and the lower die A are raised, as shown inFIG. 10C, the lower die A advances into the upper die B, and desiredprocessing, for example, drawing is performed. In this process, if theascent of the lower die A proceeds, and the forming stroke approaches anend, the existence/nonexistence of distortion on the side of the slideis detected by the displacement sensor 5 g. When it is detected that anyconvex distortion (compression deformation) has occurred on the upperside, the pressure generating means 5 c is operated by a signal from thecontrol means 5 f, and the pressure P2 higher than that at the time ofthe above touch is introduced into the pressurizing portion 5 b.Thereby, the output of the pressing member 5 e becomes strong, and asexaggeratingly shown in FIG. 13, the pressure of the lower surface ofthe slide is intensified.

Thereby, since the upper die B is directed downward and a convexdeformation force is given by a reaction force, distortion is corrected.For this reason, since the slide 3 d and the upper die B adhere to eachother, the forming force can be uniformly transmitted to a workpiece,and forming exactly suited to cavities of the dies A and B is performed,the forming shape of the workpiece becomes very good.

After the completion of forming, the slide 2 a is lowered by therotation of Servo motor 2 f, and returns the lower die A to the positionof the bolster. At this stage, a forming load is lost at this phase, andthe deflection of the slide 3 d and the upper die B disappear. Thus, thecorrection becomes unnecessary. Thus, the pressurizing portion 5 b isdecompressed by the pressure generating means 5 c, and the pressingmember 5 e is made to return to its original position. Also, if thedie-clamping press unit 3 is raised as shown in FIG. 10D and the slide 3e has stopped at a top dead center, a formed product w′ is removed, andthe processing process is completed.

As described above, as a first step, wrinkle holding pressure iscontrolled by applying pressure to the pressing member 5 e via thepressurizing portion 5 b at the time of the touch of dies. Thus,nonuniformity of the wrinkle holding force resulting from the deflectionof the wrinkle holder can be canceled in cooperation with the fact thatcushion pins are not used, and a uniform wrinkle holding state can becreated. Further, as a second step, deflection correction on the side ofthe slide can be properly performed by applying a pressure higher thanthe first step at the stroke end to the pressing member 5 e via thepressurizing portion 5 b. Moreover, re-striking forming is performed byapplying the deflection correction pressure of P2 at the stroke end.Accordingly, the precision of formed products can be significantlyimproved.

In addition, the pressure within the pressurizing portion 5 b can befreely controlled in an arbitrary position of the press by a digitalcontrol system, the torque of a servo motor, and speed control. Forexample, if the rotational direction of the servo motor 57 is reversedby an instruction from a controller and the servo motor 57 is drivenwith the torque and rotational frequency according to processingconditions, in FIG. 7, the piston 550 retreats to increase the cylindervolume. In FIG. 8, the pump 53 makes reverse rotation to switch suctionand discharge, and the pressure medium within the pipe 54 is returned toa tank according to torque and rotational frequency. Thereby, since thepressure of the pressurizing portion 5 b becomes low, the pressing forceof the pressing member 5 e is also reduced, the wrinkle holding force isrelieved, and the cushion effect suitable for drawing is exhibited tofluidize a material. Further, deepening on the detection of thedisplacement sensor 5 g and the rotational direction, torque, androtational frequency of the servo motor 57 corresponding thereto, thepressing force of the pressing member 5 e according to the deflectionstate of the press is adjusted.

The wrinkle holding pressure and deflection correction pressure can becontrolled in a stepless fashion by the torque and rotational frequencyof the servo motor 57. That is, if the torque of the servo motor 57 isreduced, deceleration is made and if the torque is increased,acceleration is made. If the rotational frequency is small, the amountof the pressure medium returned to a cylinder or a tank decreases. Thus,the reduction in the pressure within the system of the pressurizingportion 5 b is small. Accordingly, the die cushion pressure ordeflection correction pressure become relatively higher than a casewhere the rotational frequency of the servo motor is large.

Accordingly, the servo motor 57 is driven with a suitable value in thecourse of the forming stroke according to this property. Thereby,deflection can be corrected, and control to a uniform pressing force canbe made. Further, wrinkle holding pressure can be smoothly controlledwith high precision, and highly precise forming matched with processingconditions can be realized.

As can be understood from the forming stroke, the overall height of thepress can be reduced by processing stroke. Further, forming is performedby an underdrive method, using the lower forming press unit 2, and isperformed with the same minimum stroke length as the forming stroke.Therefore, energy saving can be achieved.

Also, since the driving of the forming press unit 2 transmits a verticalmotion to the slide 2 a via the eccentric links 2 e with the digitalsystem motor 2 f as a driving source, speed increase and largemagnification ratio of a force can be obtained. Further, in thisembodiment, the drive mechanism 2 b is rotary, and does not have stoptime. Thus, high cycle time of almost twice the SPM 15-18 of aconventional press is allowed.

In addition, the drive mechanism 2 b for raising or lowering the slide 2a of the forming press unit 2 is not limited to the eccentric linkmethod. FIG. 15 shows another example. In this example, a pair of rightand left toggle links 20, and a digital system motor 21 are provided.The lower die A is located at the upper surface of the bolster 4, andthe slide 2 a is linked with the lower die A via the opening of thebolster 4. The toggle link 20 is composed of a pair of right and letlinks. Each toggle link has a first link 201 one end of which is linkedto a nut 200 which is screwed to a screw shaft 205 rotated by thedigital system motor 21, a second link 202 one end of which is linked tothe bed, and a third link 203 one end of which is linked to the slide,and the other ends of the links are collected and linked together bypivots.

FIGS. 16A to 16D show a forming process when a toggle link is used asthe drive mechanism 2 b in a stepwise fashion. Since the operation andeffects of the press are the same as those described with reference toFIGS. 10A to 10D, the description thereof is omitted.

Embodiment 2

FIGS. 10 to 21 show the embodiment using another aspect as the formingprecision improving device 5. In this embodiment, the base 5 a as a mainbody of the forming precision improving device 5, as shown in FIG. 18,is not different from that of the first embodiment in that the base issuspended by the clamper 3 g such that a gap S can be formed withrespect to the slide 3 d.

In this embodiment, as shown in FIGS. 17 and 18, the pressing member 5 eis split into a first body 5 e 1 in its central region, and a secondbody 5 e 2 in a position corresponding to a wrinkle holding region. Thepressurizing portion 5 b is constituted by a first pressurizing portion5 b 1 corresponding to the first body, and a second pressurizing portion5 b 1 corresponding to the second body. The pressure generating means isconstituted by a first pressure generating means 5 c 1 for the firstpressurizing portion, and a second pressure generating means 5 c 2 forthe second pressurizing portion.

The first pressing body 5 e 1 has a disk shape, and any of thestructures shown in FIGS. 5 and 6 is adopted as the first pressurizingportion 5 b 1. As for the first pressure generating means 5 c 1 and thesecond pressure generating means 5 c 2, any of aspects in FIGS. 7 and 8is adopted. The first pressurizing portion 5 b 1 is connected with thefirst pressure generating means 5 c 1 by a channel 54.

The second pressing body 5 e 2 is composed of a plurality of fluidactuators which are disposed at intervals, in this embodiment. That is,a number of fluid pressure cylinders each including a cylinder tubeserving as a unit pressurizing portion, and a piston serving as a unitpressing member are arrayed in chambers provided at required intervalsinside the base 5 a. The fluid pressure cylinders are individuallyprovided, or are arrayed in a chamber which is widely formed as arecess. The pistons may be exposed to the upper surface of the base 5 a,or a lid or cover with a hole is mounted on every cylinder. Each of thecylinder tubes of the fluid pressure cylinder group is connected by acommunication channel (conduit) 542 and is connected to the pressuregenerating means 5 c 2 via a channel 54′.

FIG. 20A and FIG. 20B show another aspect of the second embodiment.Here, the second pressing body 5 e 2 is constructed as an annular frameas seen in plan view, and the second pressurizing portion 5 b 2 isconstructed as a chamber formed in the shape of an annular groove insidethe base 5 a. The second pressurizing portion 5 b 2 may be of a directtype as shown in FIG. 5, or may be of an indirect type using an elasticbody as shown in FIG. 6.

Since the other configurations are the same as those of the firstembodiment, the explanation thereof will be shared with the firstembodiment, and the same reference numerals will be given to the sameparts.

The second embodiment also basically has the same effects as the firstembodiment. However, in the first embodiment, the pressing member 5 eand the pressurizing portion 5 b are a single combination. Therefore,the wrinkle holding force and deflection correction force which areobtained as a uniform force is applied to the whole pressing member 5 ewill be created.

In contrast, in the second embodiment, a pressing member 2 e is splitinto a first body 2 e 1 in its central portion or inner portion, and asecond body 2 e 2 at its periphery (corresponding to each side of aproduct). Accordingly, a pressurizing portion 2 b is also split into afirst pressurizing portion 2 b 1 and a second pressurizing portion 2 b2. Thereby, the pressure of each set is individually controlled by thefirst pressure generating means 5 c 1 and the second pressure generatingmeans 5 c 2.

For this reason, pressure requirement can be made different by the firstpressurizing portion 5 b 1 and the second pressurizing portion 5 b 2.Thus, in the first step (at the time of the touch) corresponding to FIG.11A, the second pressing body 2 e 2 projects will project by a requiredstroke to press the peripheral edge of the upper edge if only the secondpressurizing portion 5 b 2 is pressurized by the second pressuregenerating means 5 c 2. Thus, a suitable wrinkle holding force can becreated and controlled. Then, in the second step (stroke end), the firstpressure generating means 5 c 1 is driven to set the pressure of thefirst pressurizing portion 2 b 1 to the pressure of P2. Thereby, sincethe first body 2 e 1 strokes to generate a large force, any deflectionof the slide 3 d by the forming load can be properly corrected. FIG. 18shows a state at this time. Referring to this drawing, a pressure mediumis supplied to the first pressurizing portion 5 b 1 and the secondpressurizing portion 5 b 2 simultaneously from the first pressuregenerating means 5 c 1 and the second pressure generating means 5 c 2,to simultaneously moving the first pressing body 5 e 1 and the secondpressing body 5 e 2, and to generate a pressing force P1+P2 of an equalor different magnitude, thereby creating the re-striking pressure.Improvements in forming precision, and energy saving can be achieved bysuch pressing.

In addition, in FIG. 17, the pressing surfaces of the first pressingbody 5 e 1 and the second pressing body 5 e 2 face the lower surface ofthe slide 3 d. However, the invention is not limited thereto. The topand bottom of the apparatus may be reversed, and as shown in FIG. 21,the pressing surfaces of the first pressing body 5 e 1 and the secondpressing body 5 e 2 may be made to face the back surface of the upperdie B. In this case, the portion of the base outside the pressurizingportion 5 b may be firmly fixed to the slide 3 d and integrated with theslide 3 d, by bolting, etc. In the case of FIG. 21, the first pressingbody 5 e 1 and the second pressing body 5 e 2 are projected by the firstpressurizing portion 2 b 1 and the second pressurizing portion 2 b,whereby pressing forces directly act on the back surface of the upperdie B, and addition of the wrinkle holding pressure and deflectioncorrection are performed.

Embodiment 3

[Fig.] FIGS. 22 to 26 show a third embodiment of the invention.

Even in this embodiment, similarly to the second embodiment, thepressing member 5 e has a first body 5 e 1 in its central region, and asecond body 5 e 2 in a position corresponding to a wrinkle holdingregion. The pressurizing portion 5 b is split into a first pressurizingportion 5 b 1 corresponding to the first body, and a second pressurizingportion 5 b 1 corresponding to the second body. The pressure generatingmeans is split into a first pressure generating means 5 c 1 for thefirst pressurizing portion, and a second pressure generating means 5 c 2for the second pressurizing portion. Further, the second pressing body 5e 2 is composed of a group of fluid-pressure cylinders disposed atintervals.

However, in this third embodiment, the first pressing body 5 e 1 whichis the first pressing body 5 e 1 in the central region, and the firstpressurizing portion 5 b 1 are also composed of a plurality of fluidpressure cylinders which are disposed at intervals.

That is, a number of fluid pressure cylinders each including a cylindertube serving as a unit pressurizing portion, and a piston serving as aunit pressing member are arrayed in chambers provided at requiredintervals inside the base 5 a. The fluid pressure cylinders areindividually provided, or are arrayed in a chamber which is widelyformed as a recess. Each of the cylinder tubes of the fluid pressurecylinder group is connected by a communication channel (conduit) 541 andis connected to the pressure generating means 5 c 1 via the channel 54.

In addition, in this embodiment, similarly to the aspect of FIG. 21, thefirst pressing body 5 e 1 and the second pressing body 5 e 2 aredisposed such that their pressing surfaces face the upper die B. In FIG.25, contrary to the above, the first pressing body 5 e 1 and the secondpressing body 5 e 2 are disposed such that their pressing surfaces facethe slide 3 d. FIG. 26 shows FIG. 25 in partially enlarged manner. Sincethe other configurations and effects are the same as those of the secondembodiment, the description thereof is omitted.

Even in this third embodiment, the first pressing body 5 e 1 and thesecond pressing body 5 e 2 are simultaneously moved at a stroke end, anda pressing force P1+P2 of an equal or different magnitude is generated,thereby creating re-striking pressure. Thus, improvements in formingprecision, and energy saving can be achieved by such press forming.

In addition, in a case where the pressing members and the pressurizingportions are individually constructed (point group), using a fluidpressure cylinder group like the second embodiment or third embodiment,fine control of a wrinkle holding force or a deflection correction forcecan be made. As a method of realizing this, the fluid pressure cylindergroup may be split into some groups, these groups may be connectedtogether by conduits, and a pressure generating means may be connectedto every group.

However, more simply, as shown in FIG. 24A, pressure receiving pieces 9are disposed on the upper surface of the upper die including the regionswhich require the pressing by the pressing members. The pressurereceptacle pieces 9 are on the same axes as pistons, and receive thepressing by the stroke of the pistons. In the places where pressing isnot required, as shown in FIG. 24B, the pressure receiving pieces arenot arranged. Otherwise, the pressure receiving pieces which havedifferent thicknesses according to the degree of necessity of a pressingforce may be disposed.

By doing so, the wrinkle holding force can be controlled locally, usingthe fluid pressure cylinder group of the same specification and withoutincreasing the number of pressure generating means. For example, in acase where a workpiece W is large, it is possible to simply realize aconstruction in which the pressing force of a straight line region canbe made relatively high to obtain a strong wrinkle holding force, andthe pressing force of a corner region can be made relatively andslightly low to weaken the wrinkle holding force slightly.

The illustrated presses are several examples of the invention, and theinvention is not limited thereto.

The same eccentric links as the forming press unit 2 may be used for thedrive mechanism 3 b of the die-clamping press unit 3. In this case, arotary single-action-type under drive press is obtained. It is needlessto say that the forming precision improving device 5 is interposed andfixed between the slide of the die-clamping press unit and the upperdie.

Moreover, the forming precision improving device 5 itself can be usedregardless of types of presses, can be applied to a general-purposemechanical press, a hydraulic press, etc. as well as the link-type servopress shown as a prior art, and can be applied to a single-action-typepress, or a double-action type press in the classification according todriving types.

Even if being applied to any of them, a pressure-equalizing effect ishigh, and a die-mating force and a wrinkle holding force become uniformregardless of deflection of presses and dies, product precisionimproves.

Further, an energy saving effect is large, and if the pressuregenerating means is also constructed like the embodiments, a reliefvalve is not used. Thus, heat is not generated within a hydrauliccircuit, and the surge pressure when the slide and a die cushion collidewith each other is low. Moreover, durability and load bearing propertiesare high.

In addition, the invention includes the following contents.

1) A forming precision improving device including, between a die and alower surface of a slide capable of ascending or descending, a disk-likebase, a pressurizing portion built in the base and connected to externalpressure generating means and supply-pressure control means, and apressing member having a pressing surface against the lower surface ofthe slide or the upper surface of the die, and facing the pressurizingportion on the side opposite to the pressing surface.

2) A forming method using a press, including interposing between anupper die and a lower surface of a slide of a press, a device includinga disk-like base, a pressurizing portion built in the base and connectedto external pressure generating means, and a pressing member having apressing surface against the lower surface of the slide or the uppersurface of the die, and an opposite surface to the pressure surfacefacing the pressurizing portion, and setting the pressing force of thepressing member by the pressurizing portion in pressing a workpiece,i.e., a pressure P1 at a stage where the slide descends and the upperdies abuts on the workpiece, and a pressure P2 at a stage where theslide has arrived at a bottom dead center, to P2>P1.

3) The aspect 2) includes an aspect in which the pressure at a stagewhere the slide descends and the upper die has abutted on the workpieceis given to only the pressing member at its peripheral edgecorresponding to the wrinkle holder, and the pressure P2 at a stagewhere the slide has arrived at the bottom dead center is given to thepressing member in its central portion.

1. An underdrive-type press comprising: an annular wrinkle holderfixedly disposed on a bed; a forming press unit including a lower dielocated inside the wrinkle holder, a slide supporting a lower die, and adrive mechanism disposed within the bed to raise or lower the slide; adrive mechanism loaded on the side of a crown, and a slide raised orlowered by the drive mechanism; a die-clamping press unit including anupper die having a clamping portion pinching a workpiece in cooperationwith the wrinkle holder at its peripheral edge; and a device applying apressing force to the upper die from its back after the last stage ofthe descent of the slide of the die-clamping press unit and the upperdie for improvements in forming precision.
 2. The underdrive-type pressaccording to claim 1, wherein the device applying a pressing force tothe upper die from its back for improvements in forming precisionincludes: a disk-like base disposed between a lower surface of the slideand the upper die; a pressurizing portion built in the base; a pressingmember having a pressing surface against the lower surface of the slide,or the back surface of the upper die, and an opposite surface to thepressure surface facing the pressurizing portion; a pressure generatingmeans disposed in a place outside the base to feed a pressurizing mediumto the pressurizing portion; and a means disposed in a place outside thebase to control the pressure of the pressurizing medium fed to thepressurizing portion from the pressure generating means.
 3. Theunderdrive-type press according to claim 2, wherein the pressing memberincludes a disk-like body with a size enough to cover a wrinkle holdingregion.
 4. The underdrive-type press according to claim 2, wherein thepressing member has a first body in its central region, and a secondbody in a position corresponding to the wrinkle holding region, thepressurizing portion has a first pressurizing portion corresponding tothe first body, and a second pressurizing portion corresponding to thesecond body, and the pressure generating means is composed of a firstpressure generating means for the first pressurizing portion, and asecond pressure generating means for the second pressurizing portion. 5.The underdrive-type press according to claim 4, wherein the first bodyhas a disk shape, and the second body has an annular frame shape in planview.
 6. The underdrive-type press according to claim 4, wherein thefirst body has a disk shape, or the first body and the firstpressurizing portion are composed of any of a plurality of fluidpressure cylinders which are connected with each other and are disposedat required intervals, and the second body and the second pressurizingportion is composed of a plurality of fluid pressure cylinders which areconnected with each other and are disposed at required intervals.
 7. Theunderdrive-type press according to claim 2, wherein the pressurizingportion is composed of a chamber body, and an elastic body built in thechamber body.
 8. The underdrive-type press according to claim 2, whereinthe pressurizing portion is composed of a chamber body, and a fluidwhich fills the chamber body.
 9. The underdrive-type press according toclaim 2, wherein a sensor for adjusting the pressure to be fed to thepressurizing portion from the pressure generating means is interposedbetween the lower surface of the slide and the back surface of the upperdie or between the base and the back surface of the upper die.
 10. Theunderdrive-type press according to claim 2, wherein the pressuregenerating means has a servo motor as a driving source.
 11. Theunderdrive-type press according to claim 1, wherein the drive mechanismof the die-clamping press unit includes a digital system motor andlinks, and the drive mechanism of the forming press unit includes adigital system motor and links.